jasonf wrote:
Im upgrading to 8.4 discs on my deluxe and was wondering if there was any benefit to upgrading to dual circuit?
If so what needs to be done....?
If I stay on the single circuit, apart from changing to 5/8th rear cylinders do I have to change anything else like the brake balance valve?
Whether you use a single circuit or dual circuit master cylinder, 8.4" discs should be used with the pressure limiting valve (FAM7821) to the rear brakes and 3/4" rear cylinders.
You can get away with smaller rear cylinders - ie. the car will still be safe, but the brake balance will be biased more to the front.
The only advantage of going to a dual circuit master cylinder is the safety one. If one circuit leaks or runs out of fluid the other curcuit still works. That's the theory anyway - I've had a leak in the rear circuit and like someone noted above, the pedal still went to the floor! That's when you pull on the hand brake, and if it's properly maintained it will stop the car surprisingly well.
The only disadvantage to a dual circuit master cylinder is the very slightly increased pedal travel before the brakes stary to come on.
BTW, contrary to popular belief FAM7821 is simply a pressure limiting valve to the rear brakes and performs the same function as the limiter which used to be installed at the rear subframe. It does not balance the pressures between front and rear, and it does not provide any safety function in the event of a leak in one circuit.